This invention relates generally to the field of magnetic data storage devices, and more particularly, but not by way of limitation, to a microwave noise testing circuit for testing data transducing heads of a disc drive.
Disc drives are used for data storage in modern electronic products ranging from digital cameras to computers and network systems. Typically a disc drive includes a mechanical portion and an electronics portion in the form of a printed circuit board assembly that controls functions of the mechanical portion while providing a communication interface to a host being serviced by the disc drive.
Typically, the mechanical portion, or head-disc assembly, has a disc with a recording surface rotated at a constant speed by a spindle motor assembly and an actuator assembly positionably controlled by a closed loop servo system for use in accessing the stored data. The actuator assembly commonly supports a magneto resistive read/write head that writes data to and reads data from the recording surface. Normally, the magneto resistive read/write head uses an inductive element, or writer, to write data to and a magneto resistive element, or reader, to read data from the recording surface.
The disc drive market continues to place pressure on the industry for disc drives with increased capacities, higher data rates and lower costs. A key aspect of achieving lower costs is an identification of marginal components as early as practical in the manufacturing process to preclude needless accrual of additional manufacturing costs and costly rework operations in subsequent processes.
A critical component of a disc drive is the magnetorestive read/write head. As each read/write head passes through manufacturing processes in preparation for use in a disc drive, costs associated with those processes accrue and contribute to the overall cost of the disc drive. By measuring characteristics of the read/write head throughout the manufacturing process, defective and marginal read/write heads can be culled from the process before additional costs are needlessly applied.
Read/write head testing methodologies such as ABHV (Analog Buffered Head Voltage) and RHBUFF (Read Head Buffered) have been employed to cull substandard read/write heads from the process. However, in application each methodology has shortcomings. The ABHV methodology involves modifications to the pre-amplifier to allow low frequency testing of the magneto-resistive element of the read/write head via a HAT tester (Head Assembly Tester) prior to assembly of the actuator assembly into a basedeck of the disc drive. Using the ABHV methodology, a bias current substantially similar to the bias current used during operation of a disc drive, is applied to the MR element. Next, the read/write head is enveloped in a magnetic field generated by an external coil, and a low frequency noise response of the read/write head is monitored. While useful, the ABHV methodology lacks sufficient selectivity to assess the condition of magnetorestive element.
The RHBUFF methodology is more selective, but requires extensive modifications to the pre-amplifier and special bias circuits, which lower the noise contribution from the bias circuits to the test results. During testing, a substantially noise free bias current is applied to the MR element and a mid-range frequency response of the MR element is monitored. Correlation between the test results of the RHBUFF methodology and actual performance of the read/write head in a disc drive environment is tentative.
As such, challenges remain and a need persists for effective techniques for identifying, testing and predicting operating characteristics of read/write heads throughout the disc drive manufacturing process. It is to this and other features and advantages set forth herein that embodiments of the present invention are directed.
As exemplified by preferred embodiments, the present invention provides a pre-amplification circuit of a disc drive adapted to provide access for measurement of a microwave noise response of a magnetoresistive element of a read/write head responding to an application of a bias current applied across the magnetoresistive element. These and various other features and advantages, which characterize the present invention, will be apparent from a reading of the following detailed description and a review of the associated drawings.